Add usage.md

Author: DuckThom

docs/usage.md

@@ -0,0 +1,36 @@
+# Usage
+
+Let's assume the configuration has a runner defined as `xml` and an importer as `product` like so:
+
+```php
+return [
+    'importers' => [
+        ...
+        'product' => App\Importers\ProductImporter::class
+        ...
+    ],
+    'runners' => [
+        ...
+        'xml' => App\Runners\XmlRunner::class
+        ...
+    ]
+];
+```
+
+We can then run the import with the included `Import` facade.
+
+```php
+    // Using the key in the config
+    \Import::runner('xml')->importer('product')->run();
+    
+    // OR
+    
+    // Creating new instances
+    \Import::runner(new XmlRunner)->importer(new ProductImporter)->run();
+```
+
+If no runner and/or importer is specified, the `default` will be used.
+
+```php
+    \Import::run();
+```